Rated 5 out of 5 stars
It's easy to convert it to ff5. like an user before explain how to do it in mac, in windows would be the same, just need winrar.
download the file .jar with chrome open it with winrar (not to extract) then open the file install.rdf with notepad and change the 3.6. for 5.0. finally save the file and close winrar.
now you have the .jar file edited so just it need to install it through the extension menu manually. it works to me